update lcc_dtmf to use media server

backport of https://github.com/jambonz/feature-server/pull/153

lib/tasks/dial.js

@@ -176,6 +176,13 @@ class TaskDial extends Task {
     return this.data.exitMediaPath;
   }
 
+  /* current media routing for this dial: MediaPath.FullMedia (anchored at the media server),
+   * PartialMedia or NoMedia (media released to the SBC)
+   */
+  get mediaPath() {
+    return this._mediaPath;
+  }
+
   get summary() {
     if (this.target.length === 1) {
       const target = this.target[0];